1. Field of the Invention
The present invention relates to a ventilation fan and more specifically, to a ventilation fan used for cooling electronic equipment or other purposes.
2. Description of the Related Art
Generally, a conventional ventilation fan includes a housing which includes a cavity portion, an impeller accommodated in the housing, a motor portion arranged to rotate the impeller, and a motor supporting portion arranged to support the motor portion. The motor portion is provided with a stator portion and a rotor portion. The rotor portion is supported via bearings in a rotatable manner with respect to the stator portion. The motor supporting portion includes a bearing supporting portion arranged to support the bearings and a stator, and a base portion coupled to the housing. With such a configuration, the motor supporting portion is supported by the housing and supports a rotatable rotor portion.
The supporting of the motor supporting portion to the housing is realized in the following way. In the case of an axial fan, the base portion of the motor supporting portion is coupled to the housing via a plurality of ribs. In the case of a centrifugal fan, the base portion of the motor supporting portion is directly coupled to the housing, or the base portion is coupled to the housing via a plurality of ribs. In addition, the housing and the motor supporting portion (i.e., the bearing supporting portion and the base portion) including the ribs may be integrally molded by a resin, thereby reducing the number of components.
In association with the increase in density of heat generating electronic components or the like mounted in the electronic equipment, the ventilation fan is required to improve its cooling performance. For this purpose, the impeller is rotated at high-speed to increase the amount of airflow.
However, as the rotation speed of the impeller is increased, vibrations caused by the rotation of the impeller are transmitted to the motor supporting potion and the housing via the bearings. As a result, the vibrations are transmitted to the actual device to which the motor is attached, so that there is concern about the occurrence of some defect in the actual device caused by the vibrations. Especially in the case when the motor supporting portion and the housing are integrally molded by a resin, it is difficult for the vibrations to be attenuated. Accordingly, the vibrations caused by the rotation of the impeller are easily transmitted to the actual device to which the motor is attached.
For solving such a problem, (JP-A-2006-57631) discloses a technique for forming a plurality of reinforcing ribs in the base portion. With such a configuration, the motor supporting portion is reinforced, so that it is possible to reduce the transmission of vibrations.
However, even when the base portion is reinforced by forming the reinforcing ribs, it is still insufficient to substantially reduce transmission of the vibrations to the housing via the base portion.